Display device having a polyimide insulating layer

ABSTRACT

A display device having a polyimide insulating layer is disclosed. The display device has a first electrode formed on a substrate, the polyimide insulating layer formed on the first electrode in such a way that the first electrode is partially exposed, and a second electrode facing the first electrode, wherein the polyimide insulating layer is a positive-type photosensitive polyimide.

TECHNICAL FIELD

This invention relates to a display device having a first electrodeformed on a substrate and a second electrode provided facing this.

TECHNICAL BACKGROUND

Light, thin, so-called flat panel displays are the subject of attentionas image display devices (displays) to replace bulky, heavy, cathode raytubes.

Liquid crystal displays (LCDs) are popular as flat panel displays, andelectrochromic displays (ECDs) are another example of similarnon-luminescent displays, while as examples of the luminescent displayswhich have recently become a focus of attention there are plasma displaypanels (PDPs) and electroluminescent displays (ELDs). Amongst theelectroluminescent displays, high brightness may be obtained with, inparticular, organic electro-luminescent displays and there isconsiderable research and development in this area due the fact that afull colour display is possible.

These flat panel displays are operated by applying a voltage, or bypassing current, between facing first and second electrodes. In suchcircumstances, since electric charge concentration readily occurs at theedge regions of electrodes with a small radius of curvature, undesirablephenomena such as dielectric breakdown and leakage currents tend tooccur at the edge regions.

In order to suppress these phenomena, covering the edge regions of thefirst electrodes with an insulating layer is known. In this way, itbecomes possible to mitigate electric field concentration at theelectrode edge regions. Furthermore, in SP-6222315, there is disclosed atechnique for further resolving the aforesaid problem by making thethickness of the insulating layer at the boundary portion where thefirst electrode is exposed by the insulating layer gradually increasewith distance from the boundary, or in other words by giving thecross-section a tapering shape, so that there is smooth build-up of theorganic thin film layer and second electrode produced by film formationafter the forming of the insulating layer.

Generally speaking, polyimides are used as the insulating layer, andnon-photosensitive, negative photosensitive and positive photosensitivetypes are known.

In the case of a non-photosensitive polyimide, in the patterning of theinsulating film numerous photolitho processes are required, namelyapplication of the polyimide precursor onto the substrate, prebaking ofthe polyimide precursor (also referred to as drying or semi-curing),application of a photoresist onto the polyimide precursor, baking of thephotoresist (also known as drying or prebaking), exposure of thephotoresist, development of the photoresist, etching of the polyimideprecursor, elimination of the photoresist, and curing of the polyimideprecursor (also referred to as post baking). Consequently, there is theproblem that the process is complex and the yield poor.

Furthermore, in order to give the insulating film cross-section atapering form, it is necessary to optimise various parameters such asthe photoresist development conditions and the polyimide precursoretching conditions, and there is the problem that the setting of suchconditions is complex.

If a photosensitive type polyimide such as a negative or positive typephotosensitive polyimide is used, then patterning of the insulatinglayer is possible without using a photoresist, and therefore it ispossible to overcome the problems of process complexity and poorness ofyield. However, with a negative type photosensitive polyimide, insteadof a direct tapering shape there tends to be formed an undercut shape orrectangular shape, so no effect is obtained in mitigating electric fieldconcentration at the edge regions. Furthermore, with regard to positivetype photosensitive polyimides, while JP-A-8-171989 discloses atechnique for introducing an o-nitrobenzyl ester group at the polyamicacid carboxyl group, this positive type photosensitive polyimide has theproblem of poor pattern processability, and it is not possible to carryout fine patterning as in the present invention.

The present invention has the objective of carrying out the patterningof an insulating layer comprising polyimide by a simple process.Furthermore, it has the objective of readily obtaining the tapered shapewhich is the desired cross-section of the insulating layer.

DISCLOSURE OF THE INVENTION

The present invention relates to a display device which is a displaydevice which includes a first electrode formed on a substrate, aninsulating layer formed on the first electrode in such a way that thefirst electrode is partially exposed, and a second electrode providedfacing the first electrode, and the insulating layer is a positive-typephotosensitive polyimide in which polymer having, as its chiefcomponent, structural units represented by the following general formula(1), and a photoacid generator, are the indispensable components.

(R¹ and R² represent divalent to octavalent organic groups having atleast two carbon atoms, and R³ and R⁴ represent hydrogen, an alkalimetal ion, an ammonium ion or an organic group with from 1 to 20carbons. R³ and R⁴ may be the same or different. m is an integer in therange 3 to 100,000, and n and o are integers in the range 0 to 2. p andq are integers in the range 0 to 4, and n+q>0.)

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1: A plan view showing an example of the form of the insulatinglayer in the present invention.

FIG. 2: A sectional view through X-X′ in FIG. 1.

FIG. 3: An enlarged sectional view of the insulating layer boundaryportion in FIG. 2.

FIG. 4: A sectional view showing the substrate with patterned firstelectrodes.

FIG. 5: A sectional view showing the positive type photosensitivepolyimide applied onto the substrate.

FIG. 6: A sectional view showing the exposure of the polyimide precursorfilm.

FIG. 7: A sectional view showing the developed polyimide precursor filmfollowing exposure.

FIG. 8: A plan view showing schematically the shadow mask forlight-emitting layer patterning.

FIG. 9: A plan view showing schematically the shadow mask for secondelectrode patterning.

FIG. 10: Infrared absorption spectrum of the insulating layer.

Explanation of the Numerical Codes 10 substrate 11 first electrode 14insulating layer 15 opening 16 boundary portion 17 exposed region 18photomask 31 mask region 32 shadow mask opening 33 reinforcing wire 34frame

OPTIMUM FORM FOR PRACTISING THE INVENTION

The present invention relates to a display device which contains a firstelectrode formed on a substrate and a second electrode provided facingthe first electrode and, specifically, it applies to, for example, LCDs,ECDs, ELDs and display devices employing organic electro-luminescentelements (organic electroluminescent devices). An organicelectroluminescent device is a display device comprising organicelectroluminescent elements which contain a first electrode formed on asubstrate, a thin film layer containing a light-emitting layercomprising at least an organic compound formed on the first electrode,and a second electrode formed on the thin film layer. In an LCD or ELD,the gap between the first electrode and the second electrode is of theseveral micron order, but in an organic electroluminescent device thethickness of the thin film layer is about 0.1 to 0.5 μm, and so the gapbetween the first electrode and the second electrode is merely of thesub-micron order. Consequently, undesirable phenomena such as theoccurrence of current leakage and dielectric breakdown due to electriccharge concentration at the electrode edge regions occur more readilywhen compared to an LCD or ELD and, furthermore, the cross-sectionalshape of the insulating layer more readily influences thecharacteristics of the display device, so the presence of the insulatinglayer becomes still more important. The insulating layer of the presentinvention, which comprises a positive-type photosensitive polyimide,functions more effectively in a display device where the gap between thefirst and second electrodes is comparatively narrow, as in an organicelectro-luminescent device.

The insulating layer of the present invention is formed to cover atleast a part of the first electrode so that the first electrode ispartially exposed, and the insulating layer is preferably formed so asto cover the edge regions of the first electrode. An example of aparticularly preferred form of the insulating layer is shown in FIG. 1and FIG. 2. There are openings 15 in which the first electrodes 11formed in the shape of stripes on substrate 10 are exposed, and theregions other than these openings are covered by insulating layer 14.That is to say, insulating layer 14 is formed so that it covers the edgeregions of first electrodes 11. Furthermore, it is preferred that whererequired the insulating layer is formed so as to shield the edge regionsof the second electrodes facing the first electrodes. With regard to theopening 15, in an organic electroluminescent device for example it maycorrespond to one light-emitting region, that is to say a pictureelement.

In the present invention, as shown in FIG. 3, it is preferred that thecross-section of the insulating layer in the boundary portion 16, wherethe insulating layer 14 exposes the first electrode 11, has a taperedshape. Here, a tapered shape means that the angle θ in the diagram isless than 90°. Now, if an organic electroluminescent device is taken asan example, in the case where the insulating layer cross-section has atapered shape, when the organic thin film layer and the second electrodeare formed after the formation of the insulating layer, these films canbe formed smoothly in the boundary portion and it is possible to reducethe film thickness non-uniformities originating in differences inheight, so that it is possible to obtain a display device with stablecharacteristics. The taper angle θ is preferably 80° or less, morepreferably 70° or less and still more preferably 45° or less.

The insulating layer is usually formed directly above and in contactwith the first electrode. However, in the case where the first electrodeis provided with a guide electrode to lower the resistance of the firstelectrode, it is possible for the insulating layer to be formed so as tocontact the guide electrode. In such circumstances, by forming theinsulating layer so that it covers the edge regions not only of thefirst electrode but also of the guide electrode, electric chargeconcentration can be effectively suppressed.

The thickness of the insulating layer is not particularly restrictedbut, taking into account ease of film formation and patterning, it isdesirable that it be in the range 0.1 to 50 μm, preferably in the range0.2 to 50 μm and more preferably in the range 0.5 to 10 μm. If theinsulating layer is comparatively thin, high precision patterningbecomes possible. Furthermore, if the insulating layer is comparativelythick then, at the time of the production of for example an organicelectroluminescent device, when carrying out patterning of thelight-emitting layer or second electrode layer by the maskvapour-deposition method it can serve as a spacer to prevent the shadowmask damaging the layer already formed on the substrate (i.e. preventmask flaws).

The insulating layer is formed straddling adjacent first electrodes, soexcellent electrical insulation properties are demanded. The volumeresistivity of the insulating layer will preferably be at least 5×10⁶Ωcm and more preferably at least 5×10⁷ Ωcm. Now, in order to enhance thedisplay device contrast, it is possible to blacken the insulating layerbut, in such circumstances, care should be taken such that theelectrical insulation is not impaired.

In the present invention, a transparent electroconductive material ispreferred as the first electrode, and it is possible to use tin oxide,zinc oxide, vanadium oxide, indium oxide, indium tin oxide (ITO) or thelike. In display applications where patterning is carried out, it ispreferred that there be used ITO-based electrodes of outstandingprocessability. In order to enhance the electroconductivity, the ITO maycontain a small amount of metal such as silver or gold.

The present invention is characterized by the fact that the insulatinglayer comprises a positive-type photosensitive polyimide. Aphotosensitive polyimide refers to a material which can undergo directpatterning utilizing the fact that the solubility in developer ofregions of the polyimide precursor which have undergone energyirradiation differs from that of un-irradiated regions, after which thepolyimide is obtained by curing. An electron beam or the like can beutilized as the irradiation energy but in most cases electromagneticwaves are employed, in particular light from the blue to the ultraviolet(UV) region. Hence, the energy irradiation is referred to as ‘exposure’.Furthermore, the elimination of particular regions of the photosensitivepolyimide precursor utilizing differences is solubility is referred toas ‘developing’. By employing a photosensitive polyimide for theinsulating layer, it is possible to markedly shorten the processrequired for the patterning of the insulating layer, in that there areno longer required the stages of application, exposure and developing ofa resist on a non-photosensitive polyimide precursor and elimination ofsaid resist following etching of the non-photosensitive polyimideprecursor, as has been required hitherto.

There are two types of photosensitive polyimide, the positive type wherethe solubility is increased by exposure and the exposed regions areeliminated, and the negative type where hardening occurs by exposure andthe un-exposed regions are eliminated. When a photosensitive polyimideprecursor undergoes exposure, light is strongly absorbed in the surfaceregion of the film, while the amount of light absorbed tends to falltowards the interior. In other words, in the case of the positive type,the solubility of the surface region of the film becomes greater thanthat of the interior, while with the negative type it is the opposite.In the present invention, it is preferred that there be used apositive-type photosensitive polyimide in that it facilitates, at afundamental level, the obtaining of an insulating layer of tapered shape

As examples of the polyimide in the present invention, there arepolyimides and their polyamic acid precursors, polybenzoxazoles andtheir polyhydroxyamide precursors, polybenzothiazoles and theirpolythiohydroxyamide precursors, polybenzimidazoles and theirpolyaminoamidoimide precursors, and also those forming polymers withoxazole rings and other cyclic structures, but there is no restrictionto these. It is preferred that there be used a polymer represented bythe following general formula (1).

(R¹ and R² represent divalent to octavalent organic groups having atleast two carbon atoms, and R³ and R⁴ represent hydrogen, an alkalimetal ion, an ammonium ion or an organic group with 1 to 20 carbons. R³and R⁴ may be the same or different. m is an integer in the range 3 to100,000, and n and o are integers in the range 0 to 2. p and q areintegers in the range 0 to 4, and n+q>0.)

As the solvent employed in the present invention, there can be employedfor example aprotic solvents such as N-methyl-2-pyrrolidone,γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide anddimethylsulphoxide, ethers such as tetrahydrofuran, dioxane andpropylene glycol monomethyl ether, ketones such as acetone, methyl ethylketone and diisobutyl ketone, esters such as ethyl acetate, propyleneglycol monomethyl ether acetate and ethyl lactate, aromatic hydrocarbonssuch as toluene and xylene, or mixtures of such solvents.

In order to enhance the adhesion to the substrate, there can be jointlyemployed a silane coupling agent, a titanium chelating agent or thelike. There is preferably added, in terms of the polymer, from 0.5 to 10parts by weight of a silane coupling agent such as methyl methacryloxydimethoxy silane or 3-aminopropyl-trimethoxysilane, or of a titaniumchelating agent or aluminium chelating agent.

It is also possible to further enhance the adhesion by treating thesubstrate. Surface treatment is carried out using a solution of 0.5 to20 parts by weight of an aforesaid coupling agent in a solvent such asisopropanol, ethanol, methanol, water, tetrahydrofuran, propylene glycolmonomethyl ether acetate, propylene glycol monomethyl ether, ethyllactate or diethyl adipate, by spin coating, immersion, spraying orevaporation, etc. Depending on the circumstances, reaction between theaforesaid coupling agent and the substrate may be promoted bysubsequently applying a temperature of from 50° C. to 300° C.

The material of the substrate in the present invention may be of anytype which permits metal for the electrodes to be provided at thesurface, such as for example a metal, glass, semiconductor, metal oxideinsulating film, silicon nitride, polymer film or the like. Glass ispreferably employed. There are no particular restrictions on thematerial of the glass, and there may be used an alkali zinc borosilicateglass, sodium borosilicate glass, soda-lime glass, low-alkaliborosilicate glass, barium borosilicate glass, borosilicate glass,aluminosilicate glass, fused quartz glass, synthetic quartz glass or thelike. Normally, there is employed alkali-free glass, or soda-lime glassgiven a barrier coat of SiO₂ or the like, so that there is littleelution of ions from the glass. Furthermore, the thickness should besufficient to maintain its mechanical strength, with at least 0.1 mm andpreferably at least 0.5 mm being adequate.

Again, where required, for the purposes of enhancing the coatingcharacteristics of the composition of the present invention on thesubstrate, there may be mixed therein a surfactant, an ester such asethyl lactate or propylene glycol monomethyl ether acetate, an alcoholsuch as ethanol, a ketone such as cyclohexanone or methyl isobutylketone, or an ether such as tetrahydrofuran or dioxane. Furthermore,there may be added silicon dioxide, titanium dioxide or other inorganicparticles, or polyimide powder, etc.

The polymer in which structural units represented by general formula (1)are the chief component can have hydroxyl groups, and the solubility inaqueous alkali solution will be better than that of a polyamic acidwithout hydroxyl groups. In particular, with regard to the hydroxylgroup type, phenolic hydroxyl groups are preferred from the point ofview of solubility in aqueous alkali solution.

The polymer represented by general formula (1) in the present inventioncan form polymer with imide rings, oxazole rings or other such cyclicstructures by heating or by means of a suitable catalyst. By formingcyclic structures, the heat resistance and solvent resistance aredramatically improved. In general formula (1), the residue whichconstitutes R¹ represents the structural component of an acid, and it isa divalent to octavalent organic group with at least two carbon atoms.From the point of view of the heat resistance of the polymer in thepresent invention, it is preferred that R¹ contains an aromatic ring oraromatic heterocyclic ring and, furthermore, that it is a divalent tooctavalent organic group with 6 to 30 carbon atoms.

In general formula (1), the residue which constitutes R² represents thestructural component of a diamine, and it is a divalent to octavalentorganic group with at least two carbon atoms. From the point of view ofthe heat resistance of the polymer in the present invention, it ispreferred that R² contains an aromatic ring or aromatic heterocyclicring and, furthermore, that it is a divalent to hexavalent organic groupwith 6 to 30 carbon atoms.

R³ and R⁴ in general formula (1) represent hydrogen, an alkali metalion, an ammonium ion or an organic group with 1 to 20 carbons. In thecase where n or o is 2, then the two R³ groups may be the same ordifferent and again the two R⁴ groups may be the same or different.

The photosensitive resin composition of the present invention may onlycomprise structural units represented by general formula (1) or it maybe a copolymer or blend with other structural units. In suchcircumstances, it is preferred that it contain at least 90 mol % ofstructural units represented by general formula (1). The type and amountof other structural units used in a copolymer or blend will preferablybe selected from within a range such that the heat resistance of thepolymer obtained by the final heat treatment temperature is notimpaired.

In the case where R³ and R⁴ are hydrogen in the polymer chieflycomprising structural units represented by general formula (1), theremay be employed the method in which a tetracarboxylic acid dianhydrideand a diamine are selectively combined, and these then reacted togetherin a polar solvent in which the chief component isN-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide,dimethylsulphoxide, hexamethyl-phosphoramide or the like, or a solventin which the chief component is γ-butyrolactone.

In the case where R³ and R⁴ are organic groups with 1 to 20 carbons, inparticular alkyl groups, there may be employed the method in which atetracarboxylic acid dianhydride is reacted with an alcohol compound,after which the acid chloride is synthesized using thionyl chloride, andthen this selectively combined with a suitable diamine, or where theselective combination with the diamine is effected using a suitabledehydrating agent such as dicyclohexylcarbodiimide, and reaction carriedout in a polar solvent in which the chief component isN-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide,dimethylsulphoxide, hexamethylphosphoramide or the like, or a solvent inwhich the chief component is γ-butyrolactone.

Furthermore, in the present invention, while there can be used anypolymer corresponding to general formula (1), from amongst such polymersthose represented by the following formulae are preferred.

R⁵ is a tetravalent organic group with at least two carbon atoms, R⁶ isa divalent organic group with at least two carbon atoms, and R⁷ and R⁸represent hydrogen, an alkali metal ion, an ammonium ion or an organicgroup with 1 to 20 carbons. R⁷ and R⁸ may be the same or different. m isan integer in the range 3 to 100,000.

R⁹ is a trivalent to octavalent organic group with at least two carbonatoms, R¹⁰ is a divalent to hexavalent organic group with at least twocarbon atoms, and R¹¹ represent hydrogen or an organic group with 1 to20 carbons. m is an integer in the range 3 to 100,000, t is 1 or 2, rand s are integers in the range 0 to 4, and r+s>0.

R¹² represents a divalent organic group with at least two carbon atoms,and R¹³ represents a tetravalent organic group with at least two carbonatoms. m is an integer in the range 3 to 100,000.

R¹⁴ represents a tetravalent organic group with at least two carbonatoms and R¹⁵ represents a tri- or tetravalent group with at least twocarbon atoms. R¹⁶ to R¹⁸ represent hydrogen, an alkali metal ion, anammonium ion or an organic group with 1 to 20 carbons. R¹⁶ to R¹⁸ may bethe same or different. u is the integer 1 or 2, and in the case where uis 2 then the two R¹⁸ groups may be the same or different. m is aninteger in the range 3 to 100,000.

In aforesaid general formula (2), R⁵ represents a tetravalent organicgroup with at least two carbon atoms. In terms of the heat resistance ofthe polymer in the present invention, it is preferred that R⁵ contain anaromatic or aromatic heterocyclic ring and, furthermore, that it is atetravalent organic group with 6 to 30 carbons. Specific examples of R⁵are the residues of 3,3′,4,4′-biphenyltetracarboxylic acid,3,3′,4,4′-diphenylethertetracarboxylic acid,3,3′,4,4′-diphenylhexafluoropropanetetracarboxylic acid,3,3′,4,4′-benzophenonetetracarboxylic acid,3,3′,4,4′-diphenylsulphonetetracarboxylic acid, pyromellitic acid,butanetetracarboxylic acid, cyclopentanetetracarboxylic acid and thelike, but there is no restriction to these. Furthermore, R⁵ may becomposed of one of these, or there may be employed copolymer composed oftwo or more types of R⁵.

In general formula (2), R⁶ is a divalent organic group with at least twocarbon atoms. In terms of the heat resistance of the polymer in thepresent invention, it is preferred that R⁶ contain an aromatic oraromatic heterocyclic ring and, furthermore, that it is a divalentorganic group with 6 to 30 carbons. Preferred specific examples of R⁶are the residues of compounds such as p-phenylenediamine,m-phenylenediamine, methyl-p-phenylenediamine,methyl-m-phenylenediamine, dimethyl-p-phenylenediamine,dimethyl-m-phenylenediamine, trimethyl-p-phenylenediamine,trimethyl-m-phenylenediamine, tetramethyl-p-phenylenediamine,tetramethyl-m-phenylenediamine, trifluoromethyl-p-phenylenediamine,trifluoromethyl-m-phenylenediamine,bis(trifluoromethyl)-p-phenylenediamine,bis(trifluoromethyl)-m-phenylenediamine, methoxy-p-phenylenediamine,methoxy-m-phenylenediamine, trifluoromethoxy-p-phenylenediamine,trifluoromethoxy-m-phenylenediamine, fluoro-p-phenylenediamine,fluoro-m-phenylenediamine, chloro-p-phenylenediamine,chloro-m-phenylenediamine, bromo-p-phenylenediamine,bromo-m-phenylenediamine, carboxy-p-phenylenediamine,carboxy-m-phenylenediamine, methoxycarbonyl-p-phenylenediamine,methoxycarbonyl-m-phenylenediamine, diaminodiphenylmethane,bis(aminomethylphenyl)methane, bis(aminotrifluoromethylphenyl)methane,bis(aminoethylphenyl)methane, bis(aminochlorophenyl)methane,bis(aminodimethylphenyl)methane, bis(aminodiethylphenyl)methane,diaminodiphenylpropane, bis(aminomethylphenyl)propane,bis(aminotrifluoromethylphenyl)propane, bis(aminoethylphenyl)propane,bis(aminochlorophenyl)propane, bis(aminodimethylphenyl)propane,bis(aminodiethylphenyl)propane, diaminodiphenylhexafluoropropane,bis(aminomethylphenyl)hexafluoropropane,bis(aminotrifluoromethylphenyl)hexafluoropropane,bis(aminoethylphenyl)hexafluoropropane,bis(aminochlorophenyl)hexafluoropropane,bis(aminodimethylphenyl)hexafluoropropane,bis(aminodiethylphenyl)hexafluoropropane, diaminodiphenylsulphone,bis(aminomethylphenyl)sulphone, bis(aminoethylphenyl)sulphone,bis(aminotrifluoromethylphenyl)sulphone,bis(aminodimethylphenyl)sulphone, bis(aminodiethylphenyl)sulphone,diaminodiphenyl ether, bis(aminomethylphenyl) ether,bis(aminotrifluoromethylphenyl) ether, bis(aminoethylphenyl) ether,bis(aminodimethylphenyl) ether, bis(aminodiethylphenyl) ether,dimethylbenzidine, bis(trifluoromethyl)benzidine, dichlorobenzidine,bis(aminophenoxy)benzene, bis(aminophenoxyphenyl)propane,bis(aminophenoxyphenyl)hexafluoropropane, bis(aminophenoxyphenyl) ether,bis(aminophenoxyphenyl) methane, bis(aminophenoxyphenyl)sulphone and thelike, and also the residues of hydrogenated such compounds, but there isno restriction to these. Furthermore, R⁸ may be composed of one ofthese, or there may be employed a copolymer composed of two or moretypes thereof.

In aforesaid general formula (2), R⁷ and R⁸ represent hydrogen, analkali metal ion, an ammonium ion or an organic group with 1 to 20carbons. Aliphatic organic groups are preferred as the organic groupwith 1 to 20 carbons, and as examples of contained organic groups thereare hydrocarbon, hydroxyl, carbonyl, carboxyl, urethane, urea and amidegroups, but there is no restriction to these. Preferred specificexamples are the methyl group, ethyl group, isopropyl group, butylgroup, tert-butyl group, ethyl methacrylate group, ethyl acrylate group,propyl methacrylate group, propyl acrylate group, ethyl methacrylamidegroup, propyl methacrylamide group, ethyl acrylamide group, propylacrylamide group and the like, but there is no restriction to these. Interms of ease of elimination and rapidity of conversion to thepolyimide, it is more preferred that R⁷ and R⁸ be hydrogen, an alkalimetal ion or an ammonium ion, with hydrogen being most preferred. Asingle type of R⁷ and of R⁸ may be used or there may be employed amixture of two or more types. Furthermore, R⁷ and R⁸ may be the same orthey may be different.

Polymer in which structural units represented by general formula (3) arethe chief component should preferably have hydroxyl groups. Where thepolymer has hydroxyl groups, because of the presence of these hydroxylgroups the solubility in aqueous alkali solution is better than that ofa polyamic acid which does not have hydroxyl groups. In particular, fromthe point of view of solubility in aqueous alkali solution, phenolichydroxyl groups are preferred.

The residue which constitutes R⁹ in general formula (3) denotes thestructural component of an acid, and it represents a trivalent tooctavalent organic group with at least two carbon atoms. This acidcomponent preferably contains an aromatic ring and, furthermore, is atrivalent to octavalent organic group with 2 to 60 carbons which hasfrom 1 to 4 hydroxyl groups. If R⁹ does not contain hydroxyl groups, itis desirable that the R¹⁰ component includes from 1 to 4 hydroxylgroups. Furthermore, it is preferred that the hydroxyl groups bepositioned next to the amide bonds. As examples, there are the followingstructures, but the present invention is not to be restricted to these.

Furthermore, for producing the residue comprising R⁹, there can be usedtetracarboxylic acids, tricarboxylic acids or dicarboxylic acids whichdo not possess hydroxyl groups. As examples of these, there are aromatictetracarboxylic acids such as pyromellitic acid,benzophenonetetracarboxylic acid, biphenyl-tetracarboxylic acid,diphenylethertetracarboxylic acid and diphenylsulphonetetracarboxylicacid, the diesters obtained by providing two of the carboxyl groupstherein with methyl or ethyl groups, aliphatic tetracarboxylic acidssuch as butanetetracarboxylic acid and cyclopentanetetracarboxylic acid,and the diester compounds formed by providing two of the carboxyl groupstherein with methyl or ethyl groups, and tricarboxylic acids such astrimellitic acid, trimesic acid and naphthalene tricarboxylic acid.

In general formula (3), the residue which constitutes R¹⁰ denotes thestructural component of a diamine. Preferred examples of R¹⁰, in termsof the heat resistance of the polymer obtained, have aromaticity and,furthermore, have one to four hydroxyl groups. If R¹⁰ does not have ahydroxyl group, it is preferred that the R⁹ component contains from 1 to4 hydroxyl groups. Furthermore, it is preferred that the hydroxyl groupsbe positioned next to the amide bonds.

Specific examples are compounds such asbis(aminohydroxyphenyl)hexafluoropropane, diaminodihydroxypyrimidine,diaminodihydroxypyridine, hydroxydiaminopyrimidine,1,3-diamino-4-hydroxybenzene, 1,3-diamino-5-hydroxybenzene,3,3′-diamino-4,4′-dihydroxybiphenyl,4,4′-diamino-3,3′-dihydroxybiphenyl,bis(3-amino-4-hydroxyphenyl)sulphone,bis(4-amino-3-hydroxyphenyl)sulphone,bis(3-amino-4-hydroxyphenyl)hexafluoropropane,bis(4-amino-3-hydroxyphenyl)hexafluoropropane,bis(4-amino-3-carboxyphenyl)methane and dihydroxybenzene, and also thosewith the following structures.

Furthermore, for producing the residue comprising R¹⁰ in general formula(3), it is possible to employ diamines which do not contain hydroxylgroups. As examples thereof, there are phenylenediamine, diaminodiphenylether, aminophenoxybenzene, diaminodiphenylmethane,diaminodiphenylsulphone, bis(trifluoromethyl)benzidine,bis(aminophenoxyphenyl)propane, bis(aminophenoxyphenyl)-sulphone and thecompounds obtained by providing the aromatic rings therein with alkylgroup or halogen atom substituents, and also aliphaticcyclohexyldiamine, methylene-biscyclohexylamine and the like. Thesediamine compounds may be used on their own or they can be used incombinations of two or more types. It is preferred that there be used nomore than 40 mol % of such diamine component. If more than 40 mol % iscopolymerized, then the heat resistance of the polymer obtained islowered.

R¹¹ in general formula (3) represents hydrogen or an organic group with1 to 20 carbons. More preferably, it is an organic group with 1 to 10carbons. If the number of carbons in R¹¹ exceeds 20 then solubility inaqueous alkali solution is lost. In terms of the stability of thephotosensitive resin solution obtained, it is preferred that R¹¹ be anorganic group, but from the point of view of the solubility in aqueousalkali solution it is preferred that it be hydrogen. In other words, itis preferred that R¹¹ be neither all hydrogen nor all organic groups. Bycontrolling the proportion of hydrogen and organic groups whichconstitutes R¹¹, the solubility rate in aqueous alkali solution may bevaried so it is possible, by such adjustment, to obtain a photosensitiveresin composition with a suitable dissolution rate. m is an integer inthe range 3 to 100,000, t is 1 or 2, r and s are integers in the range 0to 4 and, furthermore, r+s>0. If r is 5 or more, the properties of theheat-resistant resin film obtained are lowered.

Furthermore, it is also possible to adjust the amount of residualcarboxyl groups present by imidation of some of the carboxyl groups. Theextent of imidation at this time is preferably from 1% to 50%. If thepercentage imidation exceeds 50%, the absorption by the polymer of theactinic radiation used for exposure is increased and the sensitivitydecreased.

In general formula (4), R¹² represents a divalent organic group with atleast two carbon atoms. In terms of the heat resistance of the polymerin the present invention, R¹² preferably contains an aromatic oraromatic heterocyclic ring and is a divalent organic group with 6 to 30carbons. As preferred specific examples of R¹², there are the residuesof diphenylether-3,3′-dicarboxylic acid, diphenylether-3,4′-dicarboxylicacid, diphenylether-4,4′-dicarboxylic acid, isophthalic acid,benzophenone-3,3′-dicarboxylic acid, benzophenone-3,4′-dicarboxylicacid, benzophenone-4,4′-dicarboxylic acid,diphenylsulphone-3,3′-dicarboxylic acid,diphenylsulphone-3,4′-dicarboxylic acid,diphenylsulphone-4,4′-dicarboxylic acid and the like, but there is norestriction to these. Again, R¹⁴ may comprise one of these or there maybe employed copolymer in which there are two or more types thereof.

In general formula (4), R¹³ represents a tetravalent organic group withat least two carbon atoms. In terms of the heat resistance of thepolymer in the present invention, R¹³ preferably contains an aromatic oraromatic heterocyclic ring and is a tetravalent organic group with 6 to30 carbons. Preferred specific examples of R¹³ are the residues of3,3′-diamino-4,4′-dihydroxydiphenyl ether,4,4′-diamino-3,3′-dihydroxydiphenyl ether,3,4′-diamino-3,4′-dihydroxydiphenyl ether and the like, but there is norestriction to these.

Again, R¹³ may comprise one of these or there may be employed copolymerin which there are two or more types thereof.

The polybenzoxazole precursor represented by general formula (4) can beobtained by a method such as the condensation of a dihydroxydiamine anda halogenated dicarboxylic acid, or the condensation of adihydroxydiamine and a dicarboxylic acid in the presence of adehydrocondensing agent such as dicyclohexyl-carbodiimide.

In general formula (5), R¹⁴ represents a tetravalent organic group withat least two carbon atoms, and R¹⁵ represents a tri- or tetravalentorganic group with at least two carbon atoms. In terms of the heatresistance of the polymer in the present invention, R¹⁵ preferablycontains an aromatic or an aromatic heterocyclic ring and is a divalentorganic group with 6 to 30 carbons. It is desirable that four bondingpositions are present on the aromatic ring. As specific examples of R¹⁵there are oxydiphthalic acid, pyromellitic acid,benzophenone-tetracarboxylic acid, biphenyltetracarboxylic acid,naphthalenetetracarboxylic acid, pyridinetetracarboxylic acid,perylene-tetracarboxylic acid, sulphonyl-diphthalic acid,m-terphenyl-3,3′,4,4′-tetracarboxylic acid,p-terphenyl-3,3′,4,4′-tetracarboxylic acid,diphenylether-tetracarboxylic acid, diphenylsulphone tetracarboxylicacid and other such aromatic tetracarboxylic acids, and the compoundsobtained by esterification of two carboxyl groups therein with methyl orethyl groups, butanetetracarboxylic acid, cyclopentanetetracarboxylicacid and other such aliphatic tetracarboxylic acids and the compoundsobtained by esterification of two carboxyl groups therein with methyl orethyl groups, and trimellitic acid, trimesic acid,napthalenetricarboxylic acid and other such aromatic tricarboxylicacids.

In aforesaid general formula (5), R¹⁶ and R¹⁷ represent hydrogen, analkali metal ion, an ammonium ion or an organic group with 1 to 20carbons. An aliphatic organic group is preferred as the organic groupwith 1 to 20 carbons, and as examples of contained organic groups thereare hydrocarbon, hydroxyl, carbonyl, carboxyl, urethane, urea and amidegroups. Specific examples are the methyl group, ethyl group, isopropylgroup, butyl group, tert-butyl group, ethyl methacrylate group, ethylacrylate group, propyl methacrylate group, propyl acrylate group, ethylmethacrylamide group, propyl methacrylamide group, ethyl acrylamidegroup, propyl acrylamide group and the like. Preferred examples are themethyl group, ethyl group, isopropyl group, butyl group and tert-butylgroup.

In general formula (5), R¹⁵ represents a trivalent organic groupcontaining at least two carbon atoms. In terms of the heat resistance ofthe polymer in the present invention, R¹⁵ preferably contains anaromatic or aromatic heterocyclic ring and is a tri- or tetravalentorganic group with 6 to 30 carbons. Specific examples of R¹⁵ are thosederived from 2,5-diaminobenzoic acid, 3,4-diaminobenzoic acid,3,5-diaminobenzoic acid, 2,5-diaminoterephthalic acid,bis(4-amino-3-carboxyphenyl)methylene,4,4′-diamino-3,3′-dicarboxybiphenyl,4,4′-diamino-5,5′-dicarboxy-2,2′-dimethylbiphenyl and the like. Thesemay be used on their own or two or more types may be jointly employed.

Again, optionally, other diamine compounds can also be used, examples ofwhich are m-phenylenediamine, 3,4-diaminodiphenylether,3,3′-diaminodiphenylsulphone, 3,3′-diaminodiphenylsulphide,p-phenylenediamine, 4,4′-diaminodiphenyl ether,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulphone,4,4′-diaminodiphenylsulphide,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylmethane,2,2′-bis(4-aminophenyl)propane, 4,4′-methylenedianiline,4,4′-diaminodiphenylether-3-carbodiamide and other such aromaticdiamines, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and othersuch siloxane type diamines. One or a combination of two or more ofthese may be used. Now, the amount of such other diamine compound usedis preferably no more than 90 mol % in terms of the total number ofmoles of diamine compound.

It is preferred that the polymer represented by general formula (1),general formula (2), general formula (3), general formula (4) or generalformula (5) be, as far as possible, transparent to the actinic radiationused for exposure. Hence, the absorbance of the polymer at 365 nm, per 1μm, is preferably no more than 0.1. More preferably it is no more than0.08. If it exceeds 0.1, the sensitivity in terms of exposure to 365 nmactinic radiation is reduced.

Photosensitivity can be conferred on the polymer in which structuralunits represented by general formula (1) are the chief component by theaddition of a photoacid generator. In particular, this is preferablyused in polymer in which structural units represented by general formula(3), general formula (4) or general formula (5) are the chief component.

As examples of the photoacid generator employed in the presentinvention, there are diazonium salts, diazoquinone sulphonamides,diazoquinone sulphonic acid esters, diazoquinone sulphonates,nitrobenzyl esters, onium salts, halides, halogenated isocyanates,halogenated triazines, bisarylsulphonyldiazomethanes, disulphones andother such compounds which are decomposed by light irradiation andgenerate acid. In particular, o-quinonediazide compounds are preferred,since they have the effect of suppressing the aqueous solubility ofunexposed regions. Examples of such compounds are1,2-benzoquinone-2-azido-4-sulphonic acid ester or sulphonic acid amide,1,2-naphthoquinone-2-diazido-5-sulphonic acid ester or sulphonic acidamide, and 1,2-naphthoquinone-2-diazido-4-sulphonic acid ester orsulphonic acid amide. These can be obtained for example by acondensation reaction between an o-quinonediazidesulphonyl chloride suchas 1,2-benzoquinone-2-azido-4-sulphonyl chloride,1,2-naphthoquinone-2-diazido-5-sulphonyl chloride or1,2-naphthoquinone-2-diazido-4-sulphonyl chloride and a polyhydroxycompound or polyamino compound in the presence of a dehydrochlorinationcatalyst.

Examples of the polyhydroxy compounds are hydroquinone, resorcinol,pyrogallol, bisphenol A, bis(4-hydroxyphenyl)methane,2,2-bis(4-hydroxyphenyl)hexafluoropropane, 2,3,4-trihydroxybenzophenone,2,3,4,4′-tetrahydroxybenzophenone, 2,2′,4,4′-tetrahydroxybenzophenone,tris(4-hydroxyphenyl)methane, 1,1,1-tris(4-hydroxyphenyl)ethane,1-[1-(4-hydroxyphenyl)isopropyl]-4-[1,1-bis(4-hydroxyphenyl)ethyl]benzene,4-phenylmethyl-1,2,3-benzenetriol, 4-ethyl-1,3-benzenediol,4-phenylmethyl-1,3-benzenediol,4-(1-methyl-1-phenylethyl)-1,3-benzenediol,(2,4-dihydroxyphenyl)phenylmethanone,4-diphenylmethyl-1,2,3-benzenetriol, 2,4′,4″-trihydroxytriphenylmethane,2,6-bis[(2-hydroxy-5-methylphenyl)methyl]-4-methylphenol,4,4′-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]biphenol,1,1,1-tris(4-hydroxyphenyl)ethane,4,6-bis[(4-hydroxyphenyl)methyl]-1,3-benzenediol,4,4′,4″,4′″-(1,2-ethanediylidene)tetrakisphenol,2,6-bis[(4-hydroxyphenyl)methyl]-4-methylphenol,4,4′-[4-(4-hydroxyphenyl)cyclohexylidene]bisphenol,2,4-bis[(4-hydroxyphenyl)methyl]-6-cyclohexylphenol,2,2′-methylenebis[6-[(2/4-hydroxyphenyl)methyl]-4-methylphenol],2,2′-biphenol, 4,4′-cyclohexylidenebisphenol4,4′-cyclopentylidenebisphenol 2,2′-dihydroxydiphenyl ether,4,4′-dihydroxydiphenyl ether,4,4′-[1,4-phenylenebis(1-methylethylidene)]bis-[benzene-1,2-diol],5,5′-[1,4-phenylenebis(1-methylethylidene)]bis[benzene-1,2,3-triol]4-[1-(4-hydroxyphenyl)-1-methylethyl]-1,3-benzenediol,4-[1-(4-hydroxyphenyl)cyclohexyl]-1,2-benzenediol,4-[1-(4-hydroxyphenyl)cyclohexyl]-1,3-benzenediol,4-[1(4-hydroxyphenyl)cyclohexylidene]-1,2,3-benzenetriol methyl gallate,ethyl gallate and the like.

As examples of polyamino compounds, there are 1,4-phenylenediamine,1,3-phenylenediamine, 4,4′-diaminodiphenyl ether,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulphone,4,4′-diaminodiphenylsulphide and the like.

Again, as examples of polyhydroxypolyamino compounds, there are2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane,3,3′-dihydroxybenzidine and the like.

Specific examples of the photoacid generator employed in the presentinvention are o-quinonediazide compounds based on methyl3,4,5-trihydroxybenzoate,4,4′-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol,4,4′,4″-ethylidenetrisphenol,4,6-bis[(4-hydroxyphenyl)methyl]-1,3-benzenediol,4,4,4′,4′-tetrakis[(1-methylethylidene)bis(1,4-cyclohexylidene)]phenoland 4,4′-[4-(4-hydroxyphenyl)cyclohexylidene]bisphenol, where at leastone hydroxyl group is replaced by the1,2-naphthoquinonediazido-4-sulphonyl group or1,2-naphthoquinonediazido-5-sulphonyl group.

Preferably from 5 to 100 parts by weight, and more preferably from 5 to40 parts by weight of the o-quinonediazide compound is mixed per 100parts by weight of the polymer represented by general formula (1). Withless than 5 parts by weight, sufficient sensitivity is not obtained,while with more than 100 parts by weight pattern formation by lightirradiation and subsequent developing is difficult and there is thepossibility of a lowering of the heat resistance of the resincomposition.

Again, it is also possible to use a solubility regulating agent for thepurposes of adjusting the ratio of the dissolution rates of theunexposed and exposed regions. Examples of solubility regulators arepolyhydroxy compounds, sulphonamide compounds, urea compounds and thelike and, generally speaking, where they are used as solubilityregulators in positive resists, any such compound may be favourablyemployed. In particular, there is preferably used the polyhydroxycompound which is the starting material at the time of thequinonediazide compound synthesis. Specific examples are methyl3,4,5-trihydroxybenzoate,4,4′-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol,4,4′,4″-ethylidenetrisphenol,4,6-bis[(4-hydroxyphenyl)methyl]-1,3-benzenediol and4,4,4′,4′-tetrakis[(1-methylethylidene)bis(1,4-cyclohexylidene)]phenol,but there is no restriction to these.

There is preferably mixed from 1 to 100 parts by weight, and morepreferably 5 to 40 parts by weight, of the solubility regulator per 100parts by weight of the polymer represented by general formula (1). Withless than 1 part by weight, sufficient effect is not obtained, whereasif the amount exceeds 100 parts by weight there is a possibility of theheat resistance of the resin composition falling. Consequently, it ispreferred that the amount of solubility regulator be kept to the minimumrequired.

The patterning of an insulating layer employing a positive typephotosensitive polyimide can be carried out by the following process.Over the entire face of substrate 10 on which patterning of the firstelectrodes 11 has been carried out (FIG. 4), there is coated thepositive-type photosensitive polyimide precursor film (FIG. 5). Thecoating method used can be a known technique such as the spin coatingmethod, the slit die coating method, the spray method, the roll coatingmethod, the dipping method or the like. Furthermore, coating is carriedout such that the coated film thickness after drying is 0.1 to 150 μm.Preferably it is 0.5 to 20 μm.

After optional prebaking of the coated polyimide precursor, exposure iscarried out through a photomask 18 (FIG. 6). In the exposed regions 17,the solubility is increased, so that the desired polyimide pattern canbe obtained by dissolving away the exposed regions by immersion of thesubstrate in the developer, followed by curing where required (FIG. 7).

The positive type photosensitive polyimide in the present inventionpreferably has an oxazole structure in order to realize good storagestability in the precursor state and in order to achieve goodphotosensitivity and developing properties. The oxazole structure has acharacteristic infrared absorption peak in the region of 1477 cm⁻¹. Inthe polyimide, the characteristic infrared absorption peaks of the imidestructure are at 1775-80 cm⁻¹, in the region of 1725 cm⁻¹ and in theregion of 1380 cm⁻¹. Hence, it is possible to clearly distinguishbetween them.

The prebaking of the positive type photosensitive polyimide precursor inthe present invention is preferably carried out for from 1 minute toseveral hours in the range from 50° C. to 150° C. using an oven, hotplate, infrared radiation or the like. Where required, drying is alsopossible in two or more stages, such as 2 minutes at 80° C. followed by2 minutes at 120° C.

As examples of the actinic radiation used for exposure, there areultraviolet rays, visible rays, an electron beam, X-rays and the like,but the use of a mercury lamp i-line (365 nm), h-line (405 nm) or g-line(436 nm) is preferred. One type of light of such wavelength may be usedor there may be favourably employed a mixture of two or more types.

There may also be introduced a baking treatment stage prior to thedeveloping, for the purposes of raising the pattern resolution at thetime of developing and broadening the permissible range of developmentconditions. The temperature thereof is preferably in the range 50-180°C. and, in particular, more preferably 60-150° C. The time is preferablyin the range from 10 seconds to a few hours. Outside of these ranges,either reaction will not proceed or there is fear that all regions willbecome insoluble, so care is necessary.

As the developer, there is preferably employed the aqueous solution of acompound which displays alkalinity such as an aqueous solution oftetramethylammonium, diethanolamine, diethylaminoethanol, sodiumhydroxide, potassium hydroxide, sodium carbonate, potassium carbonate,triethylamine, diethylamine, methylamine, dimethylamine,dimethylaminoethyl acetate, dimethylaminoethanol, dimethylaminoethylmethacrylate, cyclohexylamine, ethylenediamine, hexamethylenediamine orthe like. An aqueous solution of tetramethylammonium hydroxide (TMAH) isespecially ideal as the developer. Furthermore, in certaincircumstances, there may be used a combination of such aqueous alkalisolution and one or more polar solvent such as N-methyl-2-pyrrolidone,N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulphoxide,γ-butyrolactone or dimethylacrylamide, alcohol such as methanol, ethanolor isopropanol, ester such as ethyl lactate or propylene glycolmonomethyl ether acetate, or ketone such as cyclopentanone,cyclohexanone, isobutyl ketone or methyl isobutyl ketone.

After developing, a rinsing treatment is carried out with water. Thisrinsing treatment may also be carried out with an alcohol such asethanol or isopropyl alcohol or ester such as ethyl lactate or propyleneglycol monomethyl ether acetate added to the water. In the developing orrinsing, an ultrasonic treatment can be carried out.

The curing is preferably carried out at a temperature in the range from200° C. to 500° C., and more preferably in the range 250° C. to 350° C.The heat treatment is carried out for from 5 minutes to 5 hours, bytemperature selection and raising of the temperature in a stepwisefashion, or selecting a temperature range and continuously raising thetemperature. As an example, heat treatment may be carried out for 30minute periods at 140° C., 200° C. and 350° C., or alternatively thereis the method of linearly raising the temperature over two hours fromroom temperature to 400° C. It is preferred that the glass transitiontemperature of the photosensitive polyimide of the present invention bebetween 260° C. and 350° C., and more preferably between 280° C. and350° C. Furthermore, it is preferred that the 5% weight loss heatingtemperature be at least 350° C. The refractive index is not particularlyrestricted but is preferably no more than 1.8.

The dielectric breakdown strength refers to the slope of the minimumpotential where the insulating material breaks down, and it denotes thevalue of the dielectric breakdown voltage divided by the distancebetween the two electrodes (thickness of the test-piece). The dielectricbreakdown strength of the photosensitive polyimide of the presentinvention is preferably at least 200 kV/mm and more preferably at least300 kV/mm, so as to make shorting due to electric charge concentrationdifficult to occur at the time of organic EL operation. Furthermore, itis preferred that when the polyimide of the present invention ismaintained at 85° C. for at least 200 hours, the reduction in thedielectric breakdown strength is no more than 10% and more preferably nomore than 5%.

The measurement of the dielectric breakdown strength is normally carriedout by producing a measurement test-piece but it can also beadvantageously measured by dismantling the device after construction ofthe display device in the present invention. Measurement is carried outbased on JIS-C-2110.

That is to say, in the case where a measurement test-piece is used, thevarnish is coated onto a metal substrate and then prebaked, after whichit is cured in a clean oven to produce the test piece. For the coating,prebaking and curing, there are preferably used conditions identical tothose for the insulating layer in the actual display device. As thematerial of the metal substrate, there may be used any material throughwhich electricity will pass such as an aluminium alloy, iron, brass,stainless steel or the like, but the use of an aluminium alloy or brassis particularly preferred. Taking the metal substrate of the test pieceas the lower electrode, the test piece is sandwiched between this and abrass electrode, and then voltage applied while raising the voltage at afixed rate until dielectric breakdown occurs, at which point the voltageis measured. This insulation breakdown voltage is divided by thethickness of the test-piece, and the dielectric breakdown strengthcalculated. The thickness of the test-piece is measured using anellipsometer or a surface roughness meter.

Furthermore, in the case where the dielectric breakdown strength ismeasured after construction of the display device, the display device isdismantled and the light-emitting display portion extracted. Thereafter,in the region where the insulating layer is coated onto the ITO, thesecond electrode and the light-emitting layer or other organic layersare dissolved/separated away using organic solvent, and the insulatinglayer exposed. The organic solvent should be one which can dissolve orseparate away the organic layers such as the light-emitting layer, butwhich does not dissolve the insulating layer. Specifically, examplesinclude ketone solvents such as acetone, halogen solvents such aschloroform and dichloroethane, and ester solvents such as ethyl acetate,but there is no restriction to these. Thereafter, where necessary, theinsulating layer is given a cleaning treatment with UV-O3. With the ITOelectrode beneath the exposed insulating layer serving as the lowerelectrode, the insulating layer is sandwiched between this and a needleelectrode as the upper electrode, and then voltage applied while raisingthe voltage at a fixed rate until dielectric breakdown occurs, at whichpoint the voltage is measured. This dielectric breakdown voltage isdivided by the thickness of the test-piece, and the dielectric breakdownstrength calculated. As the needle electrode, there is preferablyemployed any material which is thin like a needle and through whichelectricity passes. Preferably there is used a tungsten, stainless steelor other material of thickness 10 μm to 1 mm, where the radius ofcurvature of the tip region which contacts the insulating layer is 5 μmto 500 μm. The thickness of the test-piece is measured using anellipsometer or a surface roughness meter.

EXAMPLES

Below, the present invention is explained by providing examples but theinvention is not to be restricted by these examples.

Measurement of the Dielectric Breakdown Strength

1. Case Where a Measurement Test-piece is Used

The varnish was applied onto a 5 cm×5 cm×0.5 mm aluminium alloy (type1100) substrate and, after prebaking for 2 minutes at 120° C., curingwas carried out by heating under a nitrogen atmosphere in a clean ovenat 170° C. for 30 minutes and then for a further 60 minutes at 320° C.,to produce the test-piece.

The measurement was based on JIS-C-2110. Specifically, with thealuminium alloy substrate as the lower electrode, the test piece wassandwiched between this and a brass electrode, and voltage applied. Thevoltage was raised at a constant rate and the value measured whendielectric breakdown occurred. This breakdown voltage was divided by thethickness of the test-piece, and the dielectric breakdown strengthcalculated. The thickness of the test-piece was measured using a LambdaÅSTM-602J (made by Dainippon Screen Mfg Co.).

2. Case Where Measurement is Carried Out Following Production of theDisplay Device

The display device was dismantled and the light-emitting display portionremoved. Subsequently, in the region where the insulating layer wasapplied on the ITO, the second electrode and organic layers such as thelight-emitting layer were removed by dissolving or separating-away usingacetone, and the insulating layer exposed. The insulating layer was thensubjected to a UV-O3 cleaning treatment for 10 minutes. Next, with theinsulating layer interposed between the ITO electrode beneath theexposed insulating layer, as the lower electrode, and a needle electrodeW20-158-5 (produced by the Data Probe Co., tungsten, radius of curvature12.7 μm), as the upper electrode, voltage was applied. The voltage wasraised at a constant rate and the value measured when breakdownoccurred. This dielectric breakdown voltage was divided by the thicknessof the test-piece, and the dielectric breakdown strength calculated. Thethickness of the insulating layer was measured using a Surfcom 1500Asurface hardness meter (made by the Tokyo Seimitsu Co.).

Synthesis Example 1 Synthesis of the Hydroxyl-group-containing AcidAnhydride

Under a current of dry nitrogen, 18.3 g (0.05 mol) of2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BAHF) and 34.2 g (0.3mol) of glycidyl methyl ether were dissolved in 100 g of ethyl acetate,and cooled to −15° C. To this, there was added dropwise 22.1 g (0.11mol) of trimellitic anhydride chloride dissolved in 50 g of ethylacetate, such that the temperature of the reaction liquid did not exceed0° C. Following the end of the dropwise addition, reaction was carriedout for 4 hours at 0° C.

This solution was concentrated with a rotary evaporator, and then pouredinto 1 liter of toluene and the acid anhydride obtained. This is shownbelow.

Synthesis Example 2 Synthesis of the Hydroxyl-group-containing DiamineCompound

18.3 g (0.05 mol) of BAHF was dissolved in 100 ml of acetone and 17.4 g(0.3 mol) of propylene oxide, and cooled to −15° C. Next there was addeddropwise a solution of 20.4 g (0.11 mol) of 3-nitrobenzoyl chloridedissolved in 100 ml of acetone. Following the end of the dropwiseaddition, reaction was carried out for 4 hours at −15° C. and thereafterthe temperature was returned to room temperature. The solution wasconcentrated using a rotary evaporator, and the solid obtained wasrecrystallized using a mixture of tetrahydrofuran and ethanol.

30 g of the solid collected by the recrystallization was introduced intoa 300 ml stainless steel autoclave, dispersed in 250 ml of MethylCellosolve and then 2 g of 5% palladium-carbon added. Hydrogen wasintroduced using a balloon, and a reduction reaction carried out at roomtemperature. After about 4 hours,. when it was confirmed that there wasno further deflation of the balloon, the reaction was halted. Followingthe end of the reaction, filtering was carried out and the palladiumcompound which served as the catalyst was removed. Concentration wascarried out using a rotary evaporator and the diamine compound obtained.This is shown below. The solid obtained was employed directly forreaction.

Synthesis Example 3 Synthesis of Quinonediazide Compound (1)

Under a current of nitrogen, 16.1 g (0.05 mol) of BisRS-2P (commercialname, produced by the Honshu Chemical Industry Co.) and 26.9 g (0.1 mol)of 5-naphthoquinonediazide sulphonyl chloride were dissolved in 450 g of1,4-dioxane, and brought to room temperature. There was then addeddropwise 10.1 g of triethylamine mixed with 50 g of 1,4-dioxane, suchthat the interior of the system did not exceed 35° C. Following the endof the dropwise addition, stirring was carried out for 2 hours at 30° C.The triethylamine salt was filtered off and the filtrate introduced intowater. Thereafter, the precipitate which was deposited was collected byfiltering. The precipitate was dried in a vacuum dryer andquinonediazide (1) obtained.

Synthesis Example 4 Synthesis of Quinonediazide Compound (2)

Under a current of nitrogen, 15.3 g (0.05 mol) of TrisP-HAP (commercialname, produced by the Honshu Chemical Industry Co.) and 40.3 g (0.15mol) of 5-naphthoquinone-diazide sulphonyl chloride were dissolved in450 g of 1,4-dioxane and brought to room temperature. Thereafter,quinonediazide compound (2) was obtained in the same way as in SynthesisExample 3 using 15.2 g of triethylamine mixed with 50 g of 1,4-dioxane.

Synthesis Example 5 Synthesis of Quinonediazide Compound (3)

Under a current of dry nitrogen, 19.7 g (0.05 mol) of BIR-PTBP(commercial name, produced by the Honshu Chemical Industry Co.) and 26.9g (0.1 mol) of 4-naphthoquinonediazide sulphonyl chloride were dissolvedin 450 g of 1,4-dioxane and brought to room temperature. Thereafter,quinonediazide compound (3) was obtained in the same way as in SynthesisExample 3 using 10.1 g of triethylamine mixed with 50 g of 1,4-dioxane.

Synthesis Example 6

Under a current of dry nitrogen, 5.0 g (0.02 mol) of 4,4′-diaminophenylether and 1.2 g (0.005 mol) of1,3-bis(3-aminopropyl)tetramethyldisiloxane were dissolved in 50 g ofN-methyl-2-pyrrolidone (NMP). To this, 21.4 g (0.03 mol) of thehydroxyl-group-containing acid anhydride obtained in Synthesis Example 1and 14 g of NMP were added, then reaction carried out for 1 hour at 20°C., followed by 4 hours reaction at 50° C. Thereafter, a solution of 7.1g (0.06 mol) of N,N-dimethylformamide dimethyl acetal diluted with 5 gof NMP was added dropwise over 10 minutes. Following the end of thedropwise addition, stirring was carried out for 3 hours at 50° C.

2 g of quinonediazide compound (1) obtained in Synthesis Example 3 wasdissolved in 40 g of the polymer solution obtained, and photosensitiveresin varnish A obtained. When the dielectric breakdown strength ofcured film of the varnish obtained was measured using a measurementtest-piece, it was 400 kV/mm.

Synthesis Example 7

Under a current of dry nitrogen, 15.1 g (0.025 mol) of thehydroxyl-group-containing diamine obtained in Synthesis Example 2 wasdissolved in 50 g of NMP. To this, 17.5 g (0.025 mol) of thehydroxyl-group-containing acid anhydride obtained in Synthesis Example 1and 30 g of pyridine were added, and then reaction carried out for 6hours at 60° C. Following the end of the reaction, the solution wasintroduced into 2 liters of water and the precipitate of polymer solidcollected by filtering. The polymer solid was dried for 20 hours in avacuum dryer at 80° C. 10 g of the polymer solid obtained in this waywas measured out, and dissolved in 30 g of GBL along with 2 g of thequinonediazide compound (2) obtained in Synthesis Example 4, 1.5 g ofBis-Z (commercial name, produced by the Honshu Chemical Industry Co.)and 1 g of vinylmethoxysilane to obtain photosensitive resin varnish B.When the dielectric breakdown strength of cured film of the varnish wasmeasured using a measurement test-piece, it was 410 kV/mm.

Synthesis Example 8

Under a current of dry nitrogen, 27.2 g (0.045 mol) of thehydroxyl-group-containing diamine obtained in Synthesis Example 2 and1.24 g (0.005 mol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane weredissolved in 50 g of NMP. To this, 12.4 g (0.04 mol) of3,3′,4,4′-diphenylethertetracarboxylic anhydride and 21 g of NMP wereadded, and then reaction carried out for 1 hour at 20° C. and for afurther 2 hours at 50° C. Next, there was added 0.98 g (0.01 g) ofmaleic anhydride and stirring carried out for 2 hours at 50° C., afterwhich there was added dropwise over 10 minutes a solution of 14.7 g (0.1mol) of N,N-dimethylformamide diethyl acetal diluted with 5 g of NMP.Following the end of the dropwise addition, stirring was carried out for3 hours at 50° C.

1.6 g of the quinonediazide compound (3) obtained in Synthesis Example 5was dissolved in 30 g of the polymer solution obtained andphotosensitive resin composition varnish C obtained. When the dielectricbreakdown strength of cured film of the varnish obtained was measuredusing a measurement test-piece, it was 430 kV/mm.

Synthesis Example 9

Under a current of dry nitrogen, 43 g (0.17 mol) ofdiphenylether-4,4′-dicarboxylic acid and 44.7 g (0.33 mol) of1-hydroxybenzotriazole were reacted in 300 g of N,N-dimethylacetamide.73.9 g (0.15 mol) of the dicarboxylic acid derivative obtained and 61.1g (0.17 mol) of hexafluoro-2,2-bis(3-amino-4-hydroxyphenyl)propane weredissolved under a current of dry nitrogen in 500 g of NMP. Thereafter,stirring was carried out for 10 hours at 80° C.

2 g of quinonediazide compound (2) obtained in Synthesis Example 4 wasdissolved in 40 g of the polymer solution thus obtained, andphotosensitive resin composition varnish D obtained. When the dielectricbreakdown strength of cured film of the varnish was measured using ameasurement test-piece, it was 400 kV/mm.

Synthesis Example 10

Under a current of dry nitrogen, 24.8 g of3,3′,4,4′-diphenylethertetracarboxylic dianhydride and 59.3 g of n-butylalcohol were introduced into a 500 ml four-necked flask, and reactioncarried out for 5 hours at 95° C. The excess n-butyl alcohol was drivenoff under reduced pressure, and the di-n-butyl3,3′,4,4′-diphenylethertetracarboxylic acid ester obtained. Next, undera current of dry nitrogen, 95.2 g of thionyl chloride and 70.0 g oftoluene were introduced into a 300 ml four-necked flask, and reactioncarried out for 3 hours at 40° C. The excess thionyl chloride waseliminated as an azeotrope with toluene under reduced pressure. 186 g ofNMP was added and a solution of the di-n-butyl3,3′,4,4′-diphenylethertetracarboxylate ester dichloride obtained.

Next, under a current of dry nitrogen, 95.0 g of NMP, 8.5 g of3,5-diaminobenzoic acid and 4.8 g of 4,4′-diaminodiphenyl ether wereintroduced into a 500 ml four-necked flask, and dissolved by stirring.Thereafter, 12.7 g of pyridine was added and, while maintaining thetemperature at 0-5° C., the solution of di-n-butyl3,3′,4,4′-diphenylethertetracarboxylate ester dichloride was addeddropwise over 1 hour, after which stirring was continued for 1 hour. Thesolution obtained was introduced into 5 liters of water. The precipitatewas recovered and washed, then dried under reduced pressure, and thepolyamic acid n-butyl ester obtained.

30.0 g of the polyamic acid n-butyl ester, 7.5 g of the compoundobtained by reacting 2,3,4,4′-tetrahydroxy-benzophenone andnaphthoquinone-1,2-diazido-5-sulphonyl chloride at a molar ratio of ⅓,and 2 g of (p-nitrobenzyl)-9,10-diethoxyanthracene-2-sulphonate weredissolved in 45 g of NMP by stirring, and photosensitive resincomposition varnish E obtained. When the dielectric breakdown strengthof cured film of the varnish obtained was measured using a measurementtest-piece, it was 410 kV/mm.

Example 1

A glass substrate comprising alkali-free glass of thickness 1.1 mm, onthe surface of which had been formed an ITO transparent electrode filmof thickness 130 nm by a sputtering vapour-deposition method, was cut tosize 120×100 mm. Patterning was carried out by applying a photoresistonto the ITO substrate and then performing exposure and developingaccording to the usual photolithography method. After eliminating theunnecessary portions of the ITO by etching, the photoresist was removedand ITO film patterned in the form of stripes of length 90 mm and width80 μm was obtained. There were arranged 816 of these stripe-shaped firstelectrodes at a 100 μm pitch.

Next, concentration adjustment of a positive-type photosensitivepolyimide precursor (PW-1000, produced by Toray Industries Inc.) wascarried out, and then this applied by spin coating onto the substrate onwhich the first electrodes had been formed. Pre-baking was carried outfor 2 minutes at 120° C. on a hot plate. After UV exposure of this filmthrough a photomask, developing was carried out by dissolving only theexposed regions with 2.38% TMAH solution, followed by rinsing with purewater. The polyimide precursor pattern obtained was cured by heating for30 minutes at 170° C. and then for 60 minutes at 320° C. in a clean ovenunder an atmosphere of nitrogen. In this way there was formed aninsulating layer comprising photosensitive polyimide in which there werearranged in the widthwise direction 816 openings of width 70 μm andlength 250 μm at a 100 μm pitch, and 200 such openings in the lengthwisedirection at a pitch of 300 μm, with the centre region of a firstelectrode exposed in each opening as shown in FIG. 1 and the edgeregions of the first electrode covered. The thickness of the insulatinglayer was about 1 μm, and the volume resistivity was confirmed as beingat least 1×10¹⁰ Ωcm. The cross-section of the boundary portion of theinsulating layer had a tapered shape as shown in FIG. 3, and the taperangle θ was about 45°. Furthermore, when the infrared absorptionspectrum of the insulating layer was measured using a reflection mode,absorption peaks in the region of 1780 cm⁻¹ and 1377 cm⁻¹ due to theimide structure of the polyimide were found. The infrared absorptionspectrum of cured film was measured using the varnish obtained (FIG.10).

When the dielectric breakdown strength of the PW-1000 was measured usinga measurement test-piece, it was 420 kV/mm.

Next, the construction of an organic electroluminescent device wascarried out using the substrate on which the insulating film had beenformed. The thin film layer containing the light-emitting layer wasformed by the vacuum vapour deposition method based on a resistance wireheating system. The degree of vacuum at the time of the vapourdeposition was 2×10⁻⁴ Pa or below. During the vapour deposition, thesubstrate was rotated in terms of the vapour deposition source. Firstly,15 nm of copper phthalocyanine and 60 nm of bis(N-ethylcarbazole) werevapour-deposited over the entire effective substrate area, and apositive hole transport layer formed.

For the light-emitting layer patterning, there was used a shadow maskwith mask regions and reinforcing wires formed within the same plane asshown schematically in FIG. 8. The outer shape of the shadow mask was120×84 mm, and the thickness of mask region 31 was 25 μm. 272stripe-shaped openings of length 64 mm and width 100 μm were arranged ata 300 μm pitch. In each stripe-shaped opening 32, reinforcing wires 33of width 20 μm and thickness 25 μm were formed at a 1.8 mm spacing,perpendicular to the opening. The shadow mask was fixed to a stainlesssteel plate 34 of width 4 mm, of identical outer shape.

The shadow mask for the light-emitting layer was arranged to the frontof the substrate and the two then affixed together, while a ferriteplate magnet (YBM-1B, made by Hitachi Metals Ltd) was arranged to thesubstrate rear. At this time, the stripe-shaped first electrodes werepositioned in the centre of the stripe-shaped openings of the shadowmask, the reinforcing wires were positioned on the insulating layer and,furthermore, it was arranged that the reinforcing wires and theinsulating layer were in contact. Since the shadow mask was in contactwith the insulating layer, which was of high film thickness, and did notcontact the previously-formed organic layer, mask damage was prevented.In this state, by vapour deposition of 21 nm of8-hydroxyquinoline-aluminium complex (Alq3) doped with 0.3 wt %1,3,5,7,8-pentamethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene(PM546), patterning of the green light-emitting layer was effected.

Next, with the shadow mask positioned on the first electrode pattern ata position staggered by 1 pitch, patterning of the red light-emittinglayer was effected by the vapour deposition of 15 nm of Alq3 doped with1 wt % 4-(dicyanomethylene)-2-methyl-6-(julolidylstearyl)pyran (DCJT).

Again, with the shadow mask positioned on the first electrode pattern ata position staggered by 1 pitch, patterning of the blue light-emittinglayer was effected by the vapour deposition of 20 nm of4,4′-bis(2,2′-diphenylvinyl)biphenyl (DPVBi). The respective green, redand blue light-emitting layers were arranged at every threestripe-shaped first electrodes and the exposed regions of the firstelectrodes were completely covered.

Next, 35 nm of DPVBi and 10 nm of Alq3 were vapour-deposited over theentire effective area of the substrate. Thereafter, by exposure of thethin film layer to lithium vapour, doping was effected (amount by filmthickness conversion=0.5 nm).

For the second electrode patterning, there was employed a shadow mask ofstructure as shown schematically in FIG. 9 where a gap was presentbetween one face of the mask region and the reinforcing wires. Theexternal shape of the shadow mask was 120×84 mm, and the thickness inmask region 31 was 100 μm. 200 stripe-shaped openings 32 of length 100mm and width 250 μm were arranged at a 300 μm pitch. Over the maskregion there was formed a reinforcing wire mesh 33 of width 40 μm andthickness 35 μm having a regular hexagonal structure in which thespacing between two facing sides was 200 μm. The height of the gap wasequal to the thickness of the mask region and was 100 μm. The shadowmask was fixed to a stainless steel frame 34 of width 4 mm having anidentical external shape.

The second electrodes were formed by the vacuum vapour-deposition methodbased on a resistance wire heating system. The vacuum at the time of thevapour deposition was 3×10⁻⁴ Pa or below, and during the vapourdeposition the substrate was rotated in terms of the two vapourdeposition sources. In the same way as the patterning of thelight-emitting layers, the shadow mask for the second electrodes waspositioned to the front of the substrate and the two affixed together,while a magnet was arranged towards the rear. At this time, the two werepositioned so that the insulating layer matched the position of the maskportions. Patterning of the second electrodes was carried out by thevapour-deposition of aluminium at a thickness of 240 nm in this state.The patterning of the second electrodes was carried out in the form ofstripes positioned with gaps between and positioned perpendicular to theplurality of stripe-shaped first electrodes arranged with gapsin-between.

The substrate was then removed from the evaporator and held for 20minutes under a reduced pressure atmosphere by means of a rotary pump,after which it was transferred to an argon atmosphere of dew point nomore than −90° C. Under this low moisture atmosphere, sealing wascarried out by sticking together the substrate and the glass plate forencapsulation, using a curable epoxy resin.

In this way, a simple matrix type colour organic electroluminescentdevice was constructed with patterned green, red and blue light-emittinglayers formed on 816 ITO stripe-shaped first electrodes of width 80 μmand pitch 100 μm, and with 200 stripe-shaped second electrodes of width250 μm and pitch 300 μm arranged at right angles to the firstelectrodes. Since three light-emitting regions, i.e. red, green and bluelight-emitting regions, formed 1 picture element, this luminescentdevice had 272×200 picture elements at a pitch of 300 μm. Since therewas light emission only in the region where the first electrode wasexposed by the insulating layer, one light-emitting region was of arectangular shape of width 70 μm and length 250 μm.

When this display device was subjected to line-sequential driving, itwas possible to obtain excellent display characteristics. Since the edgeregions of the first electrodes were covered by insulating layer, noshorting due to electric charge concentration was noted. Furthermore,since the cross-section had a tapered shape, at the insulating layerboundary portion the thin film layer and the second electrode were notthinned and no separation was brought about, and there was smooth filmformation, so no luminescent degradation within the light-emittingregions was apparent, and stable luminescence was obtained. When, as atest of durability, the emission characteristics were evaluated afterleaving for 250 hours at 85° C., it was found that, when compared toinitially, the light-emitting regions did not become smaller andexcellent luminescence was shown.

When the display device was dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,it was 400 kV/mm.

Example 2

Example 1 was carried out in the same way up to the formation of theinsulating layer comprising the positive-type photosensitive polyimide.Next, a negative-type photosensitive polyimide precursor (UR-3100,produced by Toray Industries Inc.) was spin coated on top of thesubstrate on which the first electrodes and insulating layer had beenformed, and then baking carried out for 1 hour at 80° C. in a clean ovenunder an atmosphere of nitrogen. After UV exposure of this film througha photomask, developing was carried out by dissolving just the unexposedregions with developer liquid (DV-505, produced by Toray IndustriesInc.), and then rinsing was performed with pure water. Subsequently,curing was carried out by heating for 30 minutes at 180° C. and then for30 minutes at 220° C. under a nitrogen atmosphere in a clean oven.Partitions were formed at right angles to the first electrodes. Theseelectrically insulating partitions were positioned on the insulatinglayer, and were of length 104 mm, width 30 μm and height 4 μm. 201 werearranged at a pitch of 300 μm.

The formation of the thin film layer was carried out in the same way asin Example 1. In the formation of the second electrodes, a separatormethod was used. That is to say, angled evaporation was carried out in astate with the substrate inclined towards the vapour deposition source,and the vapour deposition of 240 nm of aluminium carried out. In theregions shielded from the evaporated material by being in the shadow ofthe partitions, there was no deposition of evaporated material, so as aresult stripe-shaped second layer patterning was effected. Sealing wasthen carried out in the same way as in Example 1.

In this way, a simple matrix type colour organic electroluminescentdevice was constructed with patterned green, red and blue light-emittinglayers formed on 816 ITO stripe-shaped first electrodes of width 80 μmand pitch 100 μm, and 200 stripe-shaped second electrodes of width 270μm and pitch 300 μm arranged at right angles to the first electrodes. Inthe same way as in Example 1, this luminescent device had 272×200picture elements at a pitch of 300 μm and a single light-emitting regionwas of rectangular shape of width 70 μm and length 250 μm.

When this display device was subjected to line-sequential driving, itwas possible to obtain excellent display characteristics in the same wayas in Example 1. Since the edge regions of the first electrodes werecovered by insulating layer, no shorting due to electric chargeconcentration was noted. Furthermore, since the cross-section had atapered shape, at the insulating layer boundary portion there was nothinning and separation of the thin film layer and second electrode, andthere was smooth film formation, so no luminescent degradation withinthe light-emitting regions was apparent and stable luminescence wasobtained.

When the display device was dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,it was 400 kV/mm.

Example 3

The same procedure was carried out as in Example 1 up to the firstelectrode patterning. Next, an insulating layer comprisingphotosensitive polyimide identical to that in Example 1 was formedexcept that by adjustment of the concentration of the positive-typephotosensitive polyimide precursor (PW-1000, produced by TorayIndustries Inc.) and then patterning in the same way as in Example 1,the thickness was about 3 μm.

Thereafter, a simple matrix type colour organic electroluminescentdevice was constructed in the same way as in Example 1. When thisdisplay device was subjected to line-sequential driving, it was possibleto obtain excellent display characteristics in the same way as inExample 1. Since the edge regions of the first electrodes were coveredby insulating layer, no shorting due to electric charge concentrationwas noted. Furthermore, since the cross-section had a tapered shape, inspite of the thickness of the insulating layer being greater than inExample 1, at the insulating layer boundary portion there was nothinning and separation of the thin film layer and second electrode, andthere was smooth film formation, so no luminescent degradation withinthe light-emitting regions was apparent and stable luminescence wasobtained. Furthermore, since the insulating layer was thicker, there waseven less susceptibility to the effects of mask flaws in the maskvapour-deposition when compared to Example 1, and practically nolight-emitting regions of unstable luminescence due to mask flaws werenoted.

When the display device was dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,it was 400 kV/mm.

Examples 4 to 8

Example 1 was repeated except that instead of using the positive-typephotosensitive polyimide precursor (PW-1000, produced by TorayIndustries Inc.), there was used varnish A (Example 4), varnish B(Example 5), varnish C (Example 6), varnish D (Example 7) or varnish E(Example 8).

Whichever varnish was used, when the display device was subjected toline-sequential driving, it was possible to obtain excellent displaycharacteristics. Since the edge regions of the first electrodes werecovered by insulating layer, no shorting due to electric chargeconcentration was noted. Furthermore, since the cross-section had atapered shape, at the insulating layer boundary portion there was nothinning and separation of the thin film layer and second electrode, andthere was smooth film formation, so no luminescent degradation withinthe light-emitting regions was apparent and stable luminescence wasobtained. Again, when as a test of durability, the emissioncharacteristics were evaluated after leaving for 250 hours at 85° C., itwas found that, compared to initially, the light-emitting regions hadnot become smaller and excellent luminescence was shown.

When the display devices were dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,the results were as shown in Table 1.

Examples 9 to 13

Simple matrix type colour organic electroluminescent devices wereconstructed in the same way as in Example 3, except that instead of thepositive-type photosensitive polyimide precursor (PW-1000, produced byToray Industries Inc.), there was used varnish A (Example 9), varnish B(Example 10), varnish C (Example 11), varnish D (Example 12) or varnishE (Example 13). When the display devices were subjected toline-sequential driving, it was possible to obtain excellent displaycharacteristics in the same way as in Example 1. Since the edge regionsof the first electrodes were covered by insulating layer, no shortingdue to electric charge concentration was noted. Furthermore, since ineach case the cross-section had a tapered shape, in spite of thethickness of the insulating layer being greater than in Example 1, atthe insulating layer boundary portion there was no thinning andseparation of the thin film layer and second electrode, and there wassmooth film formation, so no luminescent degradation within thelight-emitting regions was apparent and stable luminescence wasobtained. Furthermore, since the insulating layer was thicker, there waseven less susceptibility to the effects of mask flaws in the maskevaporation when compared to Example 1, and practically nolight-emitting regions of unstable luminescence due to mask flaws werenoted.

Comparative Example 1

Using a negative-type photosensitive polyimide precursor (UR-3100,produced by Toray Industries Inc.), an insulating layer comprisingnegative type photosensitive polyimide was formed in the same way as inthe formation of the partitions in Example 2. The thickness of theinsulating layer was about 3 μm as in Example 3, and the insulatinglayer could be obtained in the same way as in Example 3 except that theangle θ of taper of the cross-section in the boundary portion was about90° C.

Thereafter, a simple matrix type colour organic electroluminescentdevice was constructed in the same way as in Example 1. When the displaydevice was subjected to line-sequential driving, no shorting due toelectric charge concentration was noted since the edge regions of thefirst electrodes were covered by insulating layer, but since thecross-section of the insulating layer was practically rectangular, atthe boundary portion of the insulating layer the thin film region andsecond electrode tended to become thinned and luminescent degradationwithin the light-emitting regions was noted.

When the display device was dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,it was 400 kV/mm.

Comparative Example 2

Pattern processing of the insulating layer was carried out in the sameway as in Example 1 except that instead of varnish A there was used apolyimide type positive photoresist (of type having o-nitrobenzylgroups) and there was employed 2% potassium hydroxide solution as thedeveloper. However, the pattern processability was poor and the desiredinsulating layer pattern was not obtained.

Thereafter, a simple matrix type colour organic electroluminescentdevice was constructed in the same way as in Example 1. When the displaydevice was subjected to line-sequential driving, since the insulatinglayer pattern was poor, at the boundary portion of the insulating layerthe thin film layer and second electrode became thinner and separationoccurred. Shorting due to electric charge concentration, shape faults inthe light-emitting regions and luminescent degradation within thelight-emitting regions were noted.

When the display device was dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,it was 380 kV/mm.

Comparative Example 3

Pattern processing of the insulating layer was carried out in the sameway as in Example 1, except that instead of varnish A there was used apositive type novolak resist OFPR-800 (produced by the Tokyo Ohka KogyoCo.). This was applied by the spin coating method onto the substrate onwhich the first electrodes had been formed, and prebaking carried outfor 2 minutes at 80° C. on a hot plate, followed by exposure,development and rinsing, after which curing was carried out for 8minutes at 180° C. The cross-section in the insulating layer boundaryportion had a tapered shape as shown in FIG. 3 and the angle of taperwas about 45°.

Thereafter, a simple matrix type colour organic electroluminescentdevice was constructed in the same way as in Example 1. When the displaydevice was subjected to line-sequential driving, initially good lightemission was shown but when, as a test of durability, the light-emittingcharacteristics were evaluated after maintaining for 250 hours at 85°C., the light-emitting regions were reduced to about 80% compared toinitially.

When the display device was dismantled to expose the insulating layer,and the dielectric breakdown strength measured using a needle electrode,it was 280 kV/mm.

TABLE 1 Insulating Layer Durability dielectric initial after 250 Varnishbreakdown angle emission hours at name type strength of taper thicknesscharacteristics 85° C. Ex. 1 PW-1000 positive “Photoneece” 400 V/mmabout 1 μm good good 45° Ex. 2 PW-1000 positive “Photoneece” 400 V/mmabout 1 μm good good 45° Ex. 3 PW-1000 positive “Photoneece” 400 V/mmabout 3 μm good good 45° Ex. 4 varnish A employs OH-group- 380 V/mmabout 1 μm good good containing acid anhydride 45° Ex. 5 varnish Bemploys OH-group- 390 V/mm about 1 μm good good containing acidanhydride 45° and OH-group-containing diamine Ex. 6 varnish C employsOH-group- 410 V/mm about 1 μm good good containing diamine 45° Ex. 7varnish D employs OH-group- 380 V/mm about 1 μm good good containingdiamine 45° Ex. 8 varnish E employs diamine with 390 V/mm about 1 μmgood good carboxylic acid groups 45° Ex. 9 varnish A employs OH-group-380 V/mm about 3 μm good good containing acid anhydride 45° Ex. 10varnish B employs OH-group- 390 V/mm about 3 μm good good containingacid anhydride 45° and OH-group-containing diamine Ex. 11 varnish Cemploys OH-group- 410 V/mm about 3 μm good good containing diamine 45°Ex. 12 varnish D employs OH-group- 380 V/mm about 3 μm good goodcontaining diamine 45° Ex. 13 varnish E employs diamine with 390 V/mmabout 3 μm good good carboxylic acid groups 45° Comp. 1 UR-3100 negativetype photo- 400 V/mm about 3 μm luminescent — sensitive polyimide 90°degradation Comp. 2 photoresist positive type 380 V/mm  0° formation — —containing photosensitive polyimide not o- in which o-nitrobenzylpossible nitrobenzyl groups are introduced groups Comp. 3 OFPR-800novolak type positive 280 V/mm about 1 μm good emission resist 45°regions reduced 80%

Industrial Utilization Potential

The display device of the present invention, which is characterized inthat its insulating layer comprises a positive type photosensitivepolyimide, does not require the use of a photoresist as in theprior-art, and patterning of the polyimide insulating layer can becarried out simply and in fewer stages. Furthermore, since it is readilypossible to make the cross-sectional shape of the insulating layerboundary portion tapered, there is for example smooth formation of thethin film layer which is formed on top and there is no impairment of thestability of the display device characteristics.

What is claimed is:
 1. A display device comprising a first electrodeformed on a substrate, an insulating layer formed on the first electrodein such a way that the first electrode is partially exposed, and asecond electrode facing the first electrode, wherein the insulatinglayer is a positive-type photosensitive polyimide comprising a polymerhaving structural units represented by the following general formula anda photoacid generator

wherein R¹ and R² represent divalent to octavalent organic groups havingat least two carbon atoms, and R³ and R⁴ represent hydrogen, an alkalimetal ion, an ammonium ion or an organic group with from 1 to 20carbons, R³ and R⁴ may be the same or different, m is an integer in therange 3 to 100,000, and n and o are integers in the range of 0 to 2, pand q are integers in the range of 0 to 4, and n+q>0.
 2. A displaydevice according to claim 1 wherein the photoacid generator is ano-quinonediazide compound.
 3. A display device according to claim 1wherein the insulating layer is formed so as to cover the edge regionsof the first electrode.
 4. A display device according to claim 1 whereinthe cross-section of the insulating layer at the boundary portion wherethe first electrode is partially exposed has a tapered shape.
 5. Adisplay device according to claim 1 wherein the display device is adisplay device having an organic electroluminescent element containingan organic light-emitting layer between the first electrode and thesecond electrode.
 6. A display device according to claim 1 wherein thedielectric breakdown strength of the insulating layer is at least 300kkV/mm.